Due to surface fuel accumulation, Fourmile Canyon Fire burned more intensely in some treated zones

Even widely spaced trees can readily ignite and burn when crowns extend down to the forest floor near surface fuels. Photo courtesy USFS/Molly Wineteer.

This logged area in Summit County near I-70 may be more susceptible to a catastrophic crown fire because of the high concentration of surface and ladder fuels left after the treatment. Photo by Bob Berwyn.

By Bob Berwyn

SUMMIT COUNTY —A report on the 2010 Fourmile Canyon Fire will probably raise more questions than it answers for firefighters and land managers, concluding that, in some cases, the ferocious fire near Boulder may have burned more intensely in treated areas than in adjacent untreated stands.

That may have been due to the relatively high concentration of surface fuels remaining after treatments, as well as the higher wind speeds that can occur in open forests compared to those with denser canopies, Forest Service researchers concluded in the report published last month.

Up until the horrific fire storms of this summer, the Fourmile Canyon blaze was the most destructive wildfire in Colorado history measured by the number of homes lost (162), and a recently finalized U.S. Forest Service report on the Fourmile Canyon fire is eerily prescient.

The final report, done by the Forest Service’s Fort Collins-based Rocky Mountain Research Station, was issued right around the time firefighters were mopping up from this year’s even more destructive High Park and Waldo Canyon fires, which together destroyed more than 600 homes.

Foreshadowing this year’s disasters, it warned that fires in the wildland-urban interface are likely to become more frequent and more destructive, and concluded that the Fourmile Canyon Fire even burned more intensively in some areas that had previously been treated to try and mitigate the fire danger.

The report also concluded that beetle-killed trees had “little to no effect on the fuels within the area burned by the Fourmile Canyon Fire, the fire’s behavior, or the final fire size,” explaining that crown fires are “driven by abundant and continuous surface fuels rather than beetle-killed trees.”

The report also included a section describing extensive sociological research, including surveys with residents of the Fourmile Canyon area, as well as other at-risk neighborhoods.

Perhaps not surprisingly, the researchers found that the “it won’t happen to me” sentiment runs strong among people who choose to live in the wildland-urban interface. From the report:

“A critical finding was that despite their relatively high familiarity with wildfire, most respondents did not believe that characteristics of their structure and the immediate surroundings of the structure were significant factors influencing the likelihood of a wildfire damaging their property within the next 5 years.”

Only one in five residents said they believed that the condition of the trees and brush on their property and the type of house they live in contribute significantly to the chance of a wildfire damaging their property.

That feedback is somewhat discouraging to fire-safety experts, who have long emphasized that the best way for people to protect their homes is to use fireproof materials and to create a buffer zone by clearing and trimming vegetation immediately around homes.

Nearly all the residents surveyed said they had some some mitigation, with only 4 percent responding that they hadn’t taken any action.

The researchers said they weren’t able to reach any conclusions about how the effectiveness of neighborhood-level wildfire mitigation efforts. In the seven years leading up to the Fourmile Canyon Fire, about 600 acres in the area were treated, but piles of slash left behind, lack of ongoing maintenance of the treatment areas and incomplete treatments made it challenging for investigators to reach any conclusions.

In the end, the report found no evidence that fuel treatments changed the progression of the Fourmile Canyon Fire, and that the treated areas were “probably of limited value to suppression efforts on September 6.” Large quantities of surface fuels in the treatment area also rendered them ineffective in changing fire behavior.

Satellite photos taken after the fire clearly showed that the fire burned just as intensely inside treatment areas as it did in adjacent untreated stands. In some cased, the fire appears to burned more intensely in treated areas, the investigators said, explaining that additional surface fuels, as well as higher wind speeds, may have been factors. From the report:

“One clear example of this comes from near Gold Hill where the piles of slash were scattered in the understory of a thinned stand but where the intended slash burning had not yet been completed. This situation reinforces the notions that fuel treatment performance metrics should be described and treatments need to be executed as planned to be effective.”

As was seen again this summer at the High Park Fire and the Waldo Canyon Fire, the rate of the fire’s spread simply overwhelmed fire-fighting resources, leaving hundreds of homes exposed to potential ignition within just a few hours. The investigators concluded those findings suggest that simply having more engines available is not the solution to the wildland-urban interface fire problem. When those fires are burning intensely, it’s just not possible to protect all the homes in the danger zone.

Instead, the report once again calls for a change of approach — instead of increasing expensive fire protection capabilities that have proven to strategically fail during extreme wildfire burning conditions, efforts should be focused on reducing home ignition potential within the immediate vicinity of homes, the investigators concluded.

Am a little confused – I have not read the report but gather from the above synopsis that the report states surface wind speeds were higher in treated areas. I agree that wind speeds close to the ground will be higher, but I doubt wind speed above top of overstory canopy is strongly influenced by removing midstory and underbrush and those winds are strongly affecting crown fire spread. The implication in the above synopsis is that the fire was crowing through treated areas – if true, the obvious conclusion is that not enough overstory trees were removed!

Folks that understand fire behavior know that putting midstory and underbrush on the ground and leaving it there to decay will typically result in faster spread and more fuel consumption, both of which will result in higher fireline intensities. But all but the most caviler suppression folks would much rather tackle a surface fire than a crown fire. Removing ladder fuels will reduce the probability of torching and crown fire. Furthermore, many plant communities were historically open woodlands or savannas which promote an abundant and diverse ground cover so some additional thermal thinning is often part of ecosystem restoration, at least in the South.

I have to point out — having read he report — that there are a few blurred facts here.

First, the report is very clear that the treatments had no effect on fire behavior. You’d expect it to slow a fire down and it’s a disappointment that the treatments failed due to poor handling. It’s also awful that there were large burn piles left in some areas, which had an effect on an ultra-local level. However, all that is a LOT different than saying the treatments increased the intensity of fire behavior as compared to untreated areas. This is not accurate.

Second, it’s stated here that beetle kill had no effect on fire behavior because surface fuels are a much larger driver of fire severity. The bit about surface fuels is true, but the way it is stated here implies that beetle kill is not a major contributor to fire behavior in general. Page 41 of the report specifies that beetle kill was not a contributor in this particular case because there was not much of it present in the burned area. These are important distinctions to make for the sake of accurate communication with people whose lives my actually be affected by this information.

Third, the efficacy of neighborhood-level efforts could not be evaluated properly because there were not sufficient records on what was done. This, coupled with the comments on fire-safety experts, goes a long way to suggest that what we currently know about treatment of individual properties has somehow been turned on its ear. This is also patently untrue; unfortunately, I’ve run across some people who’ve cited this article in coming to that very conclusion.

Science reporting is delicate and requires the utmost commitment to accuracy, especially in cases like this where conflation can hurt people.

Thanks for the careful read and comments. I’m intensely aware that I’m reporting for people who are affected by this. I live in the heart of beetle-kill country and I don’t want any of my friends and neighbors to have a false sense of security because they cut down a few dead lodgepoles in their neighborhood.

I think we can agree that good planning, based on site-specific information, and good execution are critical to designing fuel treatment projects that actually help. In reporting on the Waldo Canyon Fire, it was clear that some of the treatments in that area helped some of the neighborhoods survive the fire.

But I’ve also seen some haphazard treatments in my area that probably won’t be effective in slowing a fire.

In think the reference to the effect of beetle-kill states pretty clearly that this is a specific reference to this particular fire. I’ve reported elsewhere about how beetle kill affects fire behavior in different ways, depending on many other factors. Science reporting shouldn’t over-simplify, and just saying that beetle kill increases fire risks or fire intensity is not accurate either.

The report says, that, in some places, the fire appeared to burn more intensely than in untreated areas, not related to slash piles, but perhaps due to other factors that are outlined report, including wind speed and perhaps more sun hitting the ground, drier fuels, etc. I think this is an important factor in designing treatments.

Probably the most important thing I left out of this story is the importance of mitigation in the home ignition zone.

No problem — and I definitely agree about oversimplification, beetle kill and haphazard treatments. As a young forester, I especially hate to see poorly-executed treatments happen, and particularly when I’m assured by those higher up that it’s fine/normal/good enough/etc.